1. Field of Invention
The present invention relates to methods and apparatus relating to a precision scribed glass master, and in particular to a modular glass reference plate assembly, which may include an array of glass reference plate panels adhered together.
2. Description of Related Art
Producing flat product glass for the display business involves many challenges. A key requirement in this process is the ability to measure product distortion due to internal stresses in large product glass plates. Typical large product glass plates range in size up to 3.2 meters square. Optical methods and gauging techniques have developed over the past several years to enable distortion measurement via optical means. Distortion measurements may be performed by comparing scribed reference marks on the product glass with scribed reference marks on a precision scribed glass master, before and after the glass shearing process. A measured difference between such scribe marks is indicative of a level of stress in the product glass.
One such measurement apparatus is a distortion gauge, which is able to measure display glass up to 3.2 meters square. Among its various parts, a distortion gauge includes a granite base, a precision scribed glass master on top of the granite base, and optical measurement equipment. In the past, a glass master comprised of a single sheet of glass was used because of small glass product sizes that were being measured. To accommodate the desire for larger product glass sizes, use of a single sheet glass master was attempted for the 3.2 meters square sizes. However, reference glass of this size presently is difficult to create and not advantageous. Even minor damage to a portion of the reference glass may require replacement of the entire single sheet. Nevertheless, it would be desirable to have a suitable glass master able to handle larger glass product sizes.
It would therefore be desirable to further scale up the quality controls applicable to the manufacture of larger product glass sheets by creating larger precision scribed glass masters, while minimizing the challenges and risks associated with such large glass reference plates.